Photographic emulsions



United States Patent 3,203,804 PHOTQGRAPHIC EMULSIGNS Abraham Bernard Qohen, Springfield, and Comer Drake Shaclrlett, Roselle, N.J., assiguors to E. L du Pont de Nemours and Company, Wilmington, Del., 2 corporation of Delaware No Drawing. Filed Feb. 27, 1962, Ser. No. 176,149 12 Claims. (Cl. 96-114) This invention relates to improved photographic silver halide emulsions, emulsion layers, and film elements embodying the same.

Photographic films for use in the graphic arts should have good dimensional stability so that when several films are overlaid, as is customary in color reproduction these films will be in register, i.e'., in exact spatial correspondence. To achieve a high degree of dimensional stability, the photographic emulsions are often coated on glass plates. More recently, hydrophobic film bases, e.g., polyethylene terephthalate, have been used for these purposes in place of glass but the base does not solve emulsion shortcomings.

An undesirable characteristic of presently available graphic arts films is the charge in image optical density which occurs from the wet to dry state. In practical use,

it is usually desirable to develop the film to the required optical density as determined by inspection or in a densitometer while the film is wet; then to stop the development. This is not an accurate method because of the inherent optical density changes that occur on drying and it is often necessary to run a development series to obtain a single negative with a desired optical density balance. Moreover, the magnitude of change in wet-to-dry densities will vary with drying conditions. The previous methods are, of course, costly and time consuming.

Attempts have been made to substitute synthetic binders for gelatin in order to improve its characteristics for graphic arts uses, but these have been only partially successful due to the unique photographic and colloidchemical properties of gelatin as a binder. Improvements in one property are usually at the expense of another and often more important property. For example, Evva, Zeitschrift fiir wissenschaftliche Photographic, Photophysik und Photochemie, 52, 1-24 (1957), describes silver halide emulsions using dextran, a polyglucose linked in the 1-6 fashion. The use of dextran alone as a binding agent for silver halide grains, however, has various drawbacks. For instance, it is difficult or impossible to set by chilling an emulsion containing dextran as the sole colloid binding agent in the manner commonly used for gelatin emulsions. A further disadvantage of dextran in its inferior protective colloid action for silver halide grains. Many other binder modifications have been suggested, but none of these provide a proper balance between the major physical and photographic properties required in graphic arts films.

An object of this invention is to provide a unique photographic silver halide emulsion and emulsion layer which retains the advantages of gelatin while overcoming certain disadvantages. Another object is to provide photographic emulsion layers and elements for the graphic arts industry which have improved dimensional stability. Another object is to provide photographic emulsion layers of improved dimensional stability in which the optical density of the developed image remains stable during change from a Wet to a dry state. A further object is to prepare emulsion layers and elements which can be dried more rapidly. Still other objects will be apparent from the following description of the. invention.

The improved gelatino-silver halide emulsions of this invention comprise, in addition to the silver halide grains,

(1) An aqueous phase containing therein as a part of said phase (a) to 85 parts by weight of gelatin and (b) 2.5 to parts by weight of a water-soluble glycan selected from the group consisting of glycans of the empirical formulae wherein the monomeric units are naturally occurring aldoses or ketoses joined through glycosidic linkages and wherein n equals 20 to 600 and (2) 10 to parts by weight of a non-aqueous phase dispersed therein of water-dispersible colloidal particles (preferably of an average diameter of less than 400 m of a substantially water-insoluble vinyl addition polymer of an ethylenically unsaturated monomer of molecular weight less than 250. There may be present minor amounts, usually less than 5% of the weight of the three binders, of various emulsion adjuvants, dispersing agents, coating aids, etc.

The novel tri-component colloid binder silver halide emulsions can be made. in various manners. In a practical process of this invention, light-sensitive silver halide or a mixture of such halides is precipitated in an aqueous photographic gelatin solution. The resulting emulsion or dispersion retains the protective colloid, and other properties of the gelatin of photographic grade. T o the precipitated silver halide emulsion, which can be washed, ripened, etc., there are added suitable sensitizers and, if

desired, other emulsion adjuvants, and the emulsion is digested. To the digested emulsion are added, separately or simultaneously, an aqueous solution or dispersion of the glycan and of the water-insoluble vinyl addition polymer. After an intimate mixture is obtained, theresulting tricomponent colloid-silver halide dispersion is coated on a suitable support, e.g., a hydrophobic film base, and the coating dried. Additional gelatin can be added along with the other two colloids to provide the required amount of gelatin in the final silver halide emulsion or dispersion.

After drying, the light-sensitive. silver halide layer is given a sensitometric exposure through a neutral density wedge, processed by developing, fixing, etc., and the image densities are read on a conventional type of densitometer. The unique tricomponent gelatin/glycan/ Water-insoluble vinyl polymer silver halide emulsion yields a clear layer which is permeable to. aqueous devel-' oping and fixing solutions as is an all-gelatin layer and has comparable photosensitometric properties because of the similarity in silver halide grain structure and; size distribution. However, its physical, dimensional and practical photographic handling properties are markedly improved. For example, the humidity coefiicient of expansion and size change during processing of the light-' sensitive silver halide to a silver image is markedly reduced. The optical density of the image in passing from the wet to the dry state is markedly stabilized so that a final dry optical density can be accurately predicted from a wet optical density reading.

Further, the drying rate of the processed, exposed film is increased, the tendency to curl at low humidities reduced, and the impact resistance and anchorage substan- .3 tially improved. These combinations of properties and results are suprising and are of commercial importance in graphic arts photographic films where thick emulsion layers are often used for continuous tone reproduction.

In a preferred process for carrying out the invention,

there are added to the gelatino-silver halide emulsion a cationic optical sensitizing dye and a latex of the waterinsoluble vinyl polymer dispersed therein by means of an amphoteric dispersing agent, preferably an amphoteric dispersing agent of the formula:

where R is an alkyl group of 12-18 carbon atoms, m is or 1, p is 2m and M is a cation selected from the group consisting of hydrogen, sodium, potassium and ammonium. In general, the dispersing agent is used in an amount from 0.5% to 15.0% by weight of the waterinsoluble vinyl polymer.

Suitable amino acid dispersing agents are disclosed in US. Patent 2,816,920, Dec. 17, 1957, and are commercially available. Two of these dispersing agents of particular interest are disodium-N-tallow-beta-iminodipropionate and the disodium N-dodecyl-beta-iminodipropionate. In the case of the former dispersing agent, tallow is a mixture of the hydrocarbon radicals oleyl, palmityl, stearyl and myristyl in order of decreasing concentration. Non-ionic as well as cationic surfactants can be used, but best results can be obtained, especially in the case of the panchromatic silver halide emulsions, by means of the amphoteric dispersing agents described above.

The glycans used in accordance with this invention can be characterized as water-soluble condensation polymers of monosaccharides joined, through splitting off of water, to form glycosidic bonds. These include both pentose and hexose derivatives according to the following empirical equations.

While in natural glycans, "11 may vary from 10 to several thousand, the preferred glycans used in practicing the invention have from 20 to 600 such units or molecular weights-in the range from 2500100,000. Glycans of weights below the lower molecular weight range are so water diffusible they tend to wash out of the films during photographic processing, while those above 100,000 molecular weight tend to be too sparingly soluble in water, incompatible with gelatin or yield solutions of too high viscosity. Viscosities of a aqueous solution at 25 C. preferably should be below 100 centipoises.

The polysaccharides used in practicing the invention have been given the generic name glycans and most of the members are commonly known by generic names in which the -ose sulfur in the parent sugar is replaced by the suflix -an, e.g., glucan or dextran, galactan, mannan, etc., but in somecases the common names are retained, e.g., inulin.

The glycans used according to the invention may be linear or branched, homoor heteroglycans according to the classification system in Table V, pages 22-26 of Polysaccharide Chemistry, R. L. Whistler and C. L. Smart, Academic Press, New York, (1953). Each repeating unit in the above empirical formulae can be considerda derivative of a naturally occurring hexose or pentose such as in which one of the hydroxyl groups reacts with the carbonyl of the same molecule to form a pyranose or furanose ring through hemiacetal formation and a glycosidic (acetal) linkage with a second hemiacetal. Corresponding ketals would be formed with ketoses.

The exact point of attachment of the glycosidic linkage 1,4, 1,6 etc.) and orientation (on or B) is not always known and does not appear to be important provided that the glycan is water soluble. Thus certain water insoluble glycans which have 1,4-B-linkages such as xylan and cellulose are specifically excluded but galactan which has a similar linkage but is water-soluble is included by this restriction to water-soluble glycans. Inulin, which is a fructan of 10w water-solubility and high viscosity, shows the desirable effects of this invention to a lesser degree than do the more soluble glycans. In addition to the sugar residues, these polysaccharides may contain up to 15% by weight of other naturally occurring protein or carbohydrate residues provided such residues do not affect their solubility or viscosity adversely.

Among the useful polyhexoses are the water-soluble mannans, galactans, fructaus (including levans) glucofructans galactomannans, laminarins, dextrans and dextrins, etc., as well as hydrolyzed water-soluble derivatives of cellulose, starch and glycogen. The dextrans which are prepared commercially by bacterial action on sucrose are a particularly preferred class of glycan for this invention. Preferred dextrins and dextrans for this invention are described in greater detail in the assignees copending cases, Jennings, Ser. No. 776,660, filed Nov. 21, 1958, US. Patent 3,063,838, Nov. 13, 1962, and Chambers, Ser. No. 826,125, filed July 10, 1959, abandoned and in counterpart British patent specification 897,497. Useful glycans containing pentoses are araban and arabogalactans.

Considerable latitude is possible in the choice of the colloid dispersion of the Water-insoluble vinyl polymers, including copolymers. A preferred class are the alkyl acrylates and methacrylates, e.g., polymers and copolymers of methyl, ethyl, butyl and ethylhexyl acrylate or methyl and butyl methacrylate. Also, acrylic or methacrylic acid can be used in the preparation of useful copolymers. With most co-monomers, no more than 10 mole percent of such an acid is used in the polymerization with the other constitutuents so that the copolymer will remain Water-insoluble. Other useful classes of vinyl monomers used to prepare water insoluble polymer and copolymer dispersions useful in accordance with this invention are the vinyl esters such as the acetate, propionate, etc., the vinyl and vinylidene halides such as vinylidene chloride; styrene and substituted styrenes; the dienes such as butadiene; acrylonitrile; alkenes such as ethylene or propylene and the like. The water insoluble polymers are free from color-former nuclei or groups and preferably are free from cyclic nuclei.

In general, the best results are obtained with vinyl monomers which yield the lowest water sensitivity and lowest modulus of elasticity. Thus, acrylates in general are preferable to methacrylates and polyethylene to polyvinylidene chloride polymers and copolymers. The vinyl polymers, in general, have an average molecular weight above 10,000.

The particle size of vinyl dispersion is important, since the intended application requires freedom from lightscattering. In general, particle sizes below the wave length of light, i.e., below 400 m would be preferred. This may be controlled by techniques of emulsion polymerization known in the art such as the use of adequate concentrations of surfactants, the mode of stirring, the concentrations of reactants, temperature, rate of additions of monomers, etc.

In order to realize the full advantages of the improved dimensional stability of the emulsions of this invention,

' it is desirable to coat the emulsions on a film base support which also has adequate dimensional stability, e.g., polymethylene terephthalates, polystyrene, polycarbonates, e.g., the polycarbonate of 2,2-bis-p-hydroxyphenyl propane, polyethylene terephthalate/isphthalate, etc. In general the polyester films include those prepared from highly polymerized esters of terephthalic acid and at least one glycol of the formula HOCH WCH OH where W is a polymethylene or alkyl-substituted polymethylene of 0 to 8 carbons, e.g., 2,2-dimethylpropylene-1,-3-or a cycloalkylene radical of 5 to 6 carbon atoms, e.g., cyclopentyl-1,3, and cyclohexyl-l,4. Copolymeric films comprising up to mole percent of aliphatic dicarboxylic acids based on total moles of acids, e.g., succinic, glutaric, adipic, hexahydroterephthalic and sebacic acids, in addition to terephthalic acid, are also useful. These supports may have various anchor layers, e.g., layers of vinylidene chloride copolymers as disclosed in US. Patent 2,779,684.

The above-described polymers or copolymers may contain a number, e.g., 1 to 12 or more, of ether groups in the polymer chain. Such ether groups may be added as part of ether containing glycol derivatives or formed by side reactions during polymerization. Also the photographic emulsions may be coated on various films, foils and plates made of glass, metal, e.g., aluminum, various waterproof papers, cellulose derivatives, e.g., cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate-butyrate, and cellulose nitrate; other superpolymers, e.g., nylon, polyvinyl chloride, poly(vinyl chloride covinyl acetate), etc.

The polymeric dispersions used in a preferred embodiment of this invention are prepared in a conventional manner, starting with a polymerizable liquid monomer. This monomer is emulsified with water by means of the dispersing agents described above, and subjected to a conventional emulsion polymerization using a free radical initiator, e.g. peroxide or a,oc'aZO bis-(isobutyronitrile). In Procedure A, to follow, there is given a description of the preparation of a particularly preferred dispersion, that of polyethylacrylate. Alternately one can use a bulk polymerization and prepare the dispersions by dispersing the molten polymer in water in the presence of a dispersing agent, such as is commonly done with polyethylene.

The invention will be further illustrated by, but is not intended to be limited to, the following procedures and examples wherein the coatings were evaluated for their humidity coefiicient of expansion, dimensional stability, density stability, impact strength, adhesion and curl, as follows:

In determining humidity coeflicient of expansion, a -inch strip of a coating is scribed with a stylus so as to produce, near each end of the strip, fiducial marks which will be in close proximity to the fiducial marks of a calibrated Invar plate when the strip and Invar plate are brought into contact with one another. The strip is then conditioned for 24 hours at a constant temperature and humidity and then, while maintained at the same conditions, placed in flat contact with the Invar plate. Two Gaertner filar micrometer microscopes, having a total magnification of 100 diameters and micrometer least count 2x10 inches, are mounted so that measurements may be obtained by means of a graduated glass scale of distances between the fiducial marks on the coating strips and the corresponding fiducial marks on the Invar plate. The Invar plate, microscope and coating -strip are all housed in a conditioning cabinet equipped with arm ports and viewing Windows. By vector addition of these distances and the known distance between the fiducial marks on the Invar plate, the distance is determined between the two fiducial marks on the strip at a known humidity. The process is repeated, with 24- hour preconditioning, to determine the distance between the strips two fiducial marks at another known humidity.

The change in length at the two humidity values divided by the average of the two lengths and divided by the difference in percent relative humidity gives the humidity coeflicient of expansion. Invar is a nickel-steel altloy.

Dimensional stability in ter-ms of processing size change is determined in a very similar manner. Distance between fiducial marks is determined on a coating strip which has been conditioned under constant temperature and humidity for 24 hours. The strip is then conventionally processed and dried, conditioned at the previous constant temperature and humidity vfor 24 hours, and measured to determine the change in distance between fiducial marks. The processing size change is calculated by dividing this change in distance by the average distance.

Density stability was deter-mined from measurements of diffuse transmission densities (American Standards Association, Standard Z3-8.2.5-1946). The density measurements were made on both wet and dry films and on films during the process of drying at various Wet lbulb temperatures of the drying air.

Values of impact strength under various conditions were obtained using an apparatus similar to that described by R. -D. Spangle-r and E. B. Cooper, Journal of Applied Physics, vol. 28, No. 3, March 1957, pages 329-333. In this apparatus, the measured quantity is the amount of energy absorbed by a film when a steel ball is projected through it. By means of photoelectric. cells, the velocity of a steel ball in free fiight can be compared with its velocity after having passed through the film being examined.

Dry adhesion of emulsion to the support was measured by the common test wherein cross-hatched lines are cut through the emulsion and a piece of pressure-sensitive tape is applied to an emulsion surface and then rapidly pulled off. Removal of a .part of the emulsion from the base indicates inferior anchorage. Wet anchorage can be determined similarly after normal photographic processing, by determining the tendency of the wet emulsion to lift oi the base when a force is applied tangentially at the edge of the cross hatched lines.

Curl was measured by determining the weight required to restore a 10" x 12" sheet of film conditioned at 20% RH and F. to a flat condition.

PROCEDURE A A 22-liter fluted reaction pot was equipped with a thermometer, anchor stirrer, three-neck adapter contain ing a gas inlet tube and two reflux condensers. The system was purged with nitrogen for 10 to 20 min. and maintained under a positive nitrogen pressure throughout the polymerization. To the pot were added 10, liters of distilled water, 484 g. of disodium-N-tallow-fi-iminodipropionate flakes (96%) and 50 g. of gelatin (used as a thermal stabilizer) with 1040 ml. of distilled water. The mixture was allowed to soak at room temperature with moderate agitation for 10-15 minutes. The stirred reaction mixture was heated by a water bath to 50-55 C. for 15-20 min. to effect solution. To the aqueous solution in the pot was added 3300 g. of ethyl-acrylate (from which the polymerization inhibitor had been removed by extraction with alkali). The stirred reaction mixture was heated by a water bath to -85 C., held for 10 min. in this temperature range and cooled to 75 C. To the reaction mixture was added 60 ml. of a 30% by weight aqueous solution of hydrogen peroxide and the temperature was held at 75 C. until the polymerization initiated. After the initial exothermic reaction had subsided (Noie: moderated with cold water as required to control excessive foaming), 1700 g. of ethyl acrylate were added to the pot. The bath temperature was adjusted to 75t3 C. and 19 m1. of a 30% by weight aqueous solution of hydrogen peroxide was added. After the second stage of the polymerization had subsided, the temperature was raised to 80-85 C. and held in this range for 2 hours. The dispersion was then heated to C., held for 10 min. and steam distilled for 1 to 2 7 hours to remove any residual monomer. The dispersion was cooled to about 50 C. and filtered through felt to remove any residue. The composition by Weight of the dispersion made by this procedure is 30% polyethyl acrylate and 2.79% disodium-N-tallow-B-iminodipropionate.

PROCELURE B A 22-liter fluted pot was equipped as described in Procedure A and purged with nitrogen in the same manner. T o the pot were added 8 liters of distilled water and 16.7 g. of a high molecular weight polyacrylamide (thermal stabilizer) which was added slowly through a long stem funnel of narrow bore and washed in with 2.5 liters of distilled Water. The mixture was stirred for 2 to 3 hours at room temperature to effect solution. To the solution of polyacrylamide in the pot were added 667 g. of a 30% by weight aqueous isopropanol solution of a surfactant of the formula which was washed in with 400 ml. of distilled Water. A two stage polymerization was carried out as described in Procedure A except that butyl acrylate was used in place of ethyl acrylate. The composition by weight of the dispersion made by this procedure is 30% polybutyl acrylate and 1.2% polyether sulfate surfactant.

PROCEDURE C Procedure B was essentially repeated except that 800 g. of a 25% by weight aqueous solution of Tamol 371 (registered trade name, Rohm and Haas, defined by Haynes, Chemical Trade Names and Commercial Synonyms, 2nd edition, 1955, Van Nostrand and Co., New York, as the sodium salt of a carboxylated polyelectrolyte) which was washed in with 267 ml. of distilled water was used in place of the sodium salt of a polyether sulfate surfactant. A two-stage polymerization was carried out as described in Procedure A except that methyl methacrylate was used in place of ethyl acrylate. The composition by weight of the dispersion made by this procedure is polymethyl methacrylate and 1.2% sodium salt of a carboxylated polyelectrolyte.

PROCEDURE D Procedure A was essentially repeated except that 716 g. of a 28% by weight aqueous solution of a surfactant of the formula which Was washed in with 714 ml. of distilled water, was used in place of disodium-N-tallow-,G-iminodipropionate. A mixture of monomers consisting of 3500 g. of

vinylidene chloride and 1500 g. of 2-ethylhexyl acrylate Example I A high contrast silver iodobromide emulsion was prepared by combining solutions of silver nitrate, ammonium bromide and potassium iodide in a conventional manner using 14.7 g. of gelatin as a protective colloid per mole of silver halide. The emulsion was divided into two parts, A and B, and freed of unwanted soluble salts by conventional photographic washing procedures. Each emulsion was digested in the presence of the usual chemical sensitizers and carbocyanine dyes to give them panchromatic sensitivity. At the end of digestion, there was added to emulsion A, 191 g. per mole of silver halide of additional gelatin, but to emulsion B there was added, per mole of silver halide, only 126 g. of additional gelatin plus a combination of 40 g. of dextran (average M.W. about 75,000) and 223 g. of the 30% polyethyl acrylate dispersion prepared as in Procedure A. Conventional postdigestion additives (antifoggants, wetting agents, halide etc.) were added to both emulsions. Each emulsion was coated on 7-mil biaxially oriented polyethylene terephthalate film base as described in Example IV of Alles, U.S. 2,779,684 to yield a layer of silver halide containing 63 mg./dm. of silver. Each film was coated on the reverse surface with a layer containing conventional antihalation dyes. The backing binder which was equal to mg./dm. consisted of gelatin for film A and consisted of one part of gelatin to two parts of dispersed polyethyl acrylate for film B. A third film, film C, was a commercially available all-gelatin film with characteristics similar to film A and was used as a second control. A conventional, square-root-of-two stepwedge was used to expose all 3 films in a standard sensitometer. The films were then developed in a conventional metol-hydroquinone developer, fixed in a Na S O hardening fixer and washed. The diffuse transmission densities (American Standards Association, Standard Z38.2.5-1946) were measured on the wet film and this measurement was repeated on the dry film. This determination was obtained from the average values of four duplicate sets for each film to insure representative measurements. These were then evaluated as a function of the wet bulb temperature of the drying air, i.e. the film temperature during drying was varied from 70 to F. in 10 F. increments. The density changes expressed in percent of wet density for these 3 films are listed in Table I.

The data illustrate the small (and nearly constant) density changes of film B, containing the modified binder of this invention, as opposed to the conventional films with all-gelatin binders, A and C. The latter exhibit an abrupt change from to at a critical temperature which is characteristic for films with conventional gelatin binders. In addition to these improvements in density stability, Table IV also shows that the humidity coefficient of expansion between 30 and 80% RH at 70 F. of film B (containing dextran and a polyethyl acrylate dispersion) i was much lower than of the all gelatin films A and C..

Film B also showed better anchorage of the emulsion to the base, less curl and dried much faster than films At or C. 1 Example II Example I was repeated in all respects except that the silver halide precipitation was carried out in the manner used in the art to produce a low contrast emulsion. As in Example I, the emulsion was divided into two parts,

9 D and E. To part D was added only gelatin and to part E, a polyethyl acrylate dispersion and dextran. The same types of coatings were produced to yield films D and E.

Evaluation of these films, as in Example I, showed that the density stability of film E from the wet-to-dry state was much greater than that of the control film D. Similarly the dimensional stability, impact strength and drying rate of film E were superior to film D.

Example III Films of Example I were further tested. Each film was exposed and processed and the optical densities read while wet in the vicinity of 1.0 and 2.0 foreach film in the manner shown in Example I. Each film was allowed to dry in a room conditioned as follows:

Wet bulb temperature F 57 Dry bulb temperature F 71 Relative humidity percent 40 Changes in densities were recorded at two-minute intervals. For this purpose, the film was considered dry when the density no longer changed. Each film was then rewet and the density reading sequence repeated during the second drying. The results are shown in Table II. It is The same four films were then processed as in Example I and dried at four different wet bulb temperatures, while maintaining the relative humidity (RH) constant.

The interaction of the'dextran and' the dispersed polymer on stabilizing the density is very apparent in this example. Note that films H, G and I show much less sensitivity to the change in drying conditions between 90 and 100 F. The dextran appears to aifect mainly the level of the curve and the dispersed polymer affects its shape. arrives at a level of dextran and latex which gives essentially a Zero change in density from the wet-to-dry state :at a density of 2.0 over the entire drying range.

Example V two fiducial marks at the ends of a A" x 10" film strip using a pair of microscopes fitted with filar micrometers. The results are shown in Table IV below.

. clear that film B shows much less fluctuation 1n dens1ty 2 from the wet to dry state than film A, either on the first drying or on subsequent rewetting and drying. Further, film B dries much more rapidly than film A.

First drying Second drying Wet Max. Dry Drying Rewet Dry Dry dens. dens. dens. time dens. dens. tuue (ruin) (1111K) Density at about 1.0;

FilmA 1.25 1.30 1.18 22 1.08 1.16 22 FilmB 1.19 1.20 1.17 14 1.14 1.13 Density at about 2.0:

ilmA 2.23 2. 32 2.14 1. 94 2.08 20 FilmB 2.00 2.05 2.02 14 1.94 1.96 12 Example IV TABLE IV [Humidity coelficient of expansion in.lin./percent RH] A blue-sensitive silver iodobromide emulsion was prepared in a conventional manner by mixing solutions of Average silver nitrate, ammonium bromide and potassium iodide Range 1n the presence of 14.6 g. gelatin per mole of s1lver halide produced. After freeing of unwanted soluble salts by 50 Film A L62 M4 L42 243 282 the process of Moede, US. 2,772,165, and di esting 1n a FilmB 1. 73 2. 60 1. 2; 1.86 1. as

conventional manner in the presence of 133 g. of total gelatin per mole of silver halide, the emulsion was divided into 4 portions. Dextran (average mol. wt. 75,000) and a polyethyl acrylate dispersion as prepared in Procedure A were added in the proportions shown in Table III and the films were coated as in Example I to yield the following results. Contrasts and relative speeds were obtained from conventional curves of optical density vs. log

1 Calculated as weight of the pure compound in the 30% dispersion. Data obtained at wet bulb temperature of 90F.

These results indicate that the humidity coefficient of expansion of film B, having the special binder, is much less sensitive than that of film A to changes in humidity. Also film B has a lower average value of this coefficient from 30-80% relative humidity-than does conventional film A.

Example VI A panchromatically sensitized, silver iodobromide emulsion was prepared similarly to that in Example 1 except that the silver halide precipitation was carried out in the manner used in the art to produce a medium contrast emulsion. At the end of digestion sufficient gelatin was added tothe emulsion to bring the total concentration of gelatin to 133 g. per mole of silver halide. After removing a portion of the emulsion to serve as an all-gelatin control, 223 g. per mole of silver halide of a 30% by weight colloidal dispersion of polyethyl acrylate (prepared as in Procedure A) was added to the remainder of the emulsion, this being equivalent to 67 g. of pure polyethyl acrylate. The emulsion was then split into a number of portions and to each portion was added, per mole of silver halide, a polysaccharide in the amount shown in By interpolation between these three curves, one

Table V below. The emulsions were coated as in EX- ample I.

TABLE V Weight of binder per mole of AgX Rel. Wet-to-dry* Impact Polysaccharide Speed Contrast density Curl resistance Gelatin Polysac- Polyethyl change charide acrylate 133 0 1. 0 1. 4 G 133 40 67 1. 3 1. A. 133 67 67 I. 6 1. 7 B 133 40 67 1. 7 1. 9 B 133 67 67 1. 7 1. 7 133 40 67 1. 9 1. 9 C 133 67 67 2. 0 2. 0 133 40 67 1. 7 2. 2 C 133 67 67 1. 3 1. 4 133 40 67 1. 5 1. 4 A 133 67 67 I. 7 1. 8

*At optical density=2.0.

In obtaining the data in the above table, the films were evaluated as in Example IV. Cunl and impact resistance were determined as described earlier in the specification. It can be seen that the modified binder causes. an increase in speed and contrast, improved wet-to-dry density stability and improved curl and impact resistance. It is also noted that, with the various polysaccharides used, there was a difference in the concentration required for optimum density stability. In the case of araban, density stability is improved with increasing concentration and the results indicate that still higher concentrations would be needed to achieve the stability of the better glycans (polysaccharides) Example VII Example VI was repeated through the steps of adding Example VIII Example VI was repeated through the steps of adding gelatin up to a concentration of 133 g. per mole of silver halide and removing a portion of the emulsion to serve as an all-gelatin control. Forty grams of dextran per mole of silver halide was added to the remainder of the emulsion which was then divided into four portions. To each of the four portions there was added 223 g. per mole of silver halide of one of the 30% by weight colloidal dispersions of a polymer prepared, respectively, according to Procedures A, B, C and D. This was equivalent to the addition of 67 g. of the pure polymer per mole of silver halide. The emulsions were then coated and evaluated as in Example VI, giving the following results.

TABLE VII Wet-to- Impact Gela- Poly- Dex- Reladry Resis- Dispersed Polymer Dispersing Agent tin mer tran tive density tance,

speed stabildynes/ ity cm. 1

N N 133 0 0 1. 0 11 53 Polyethyl acrylate Imintodipropio- 133 67 1. 4 0 65 11a e. Polybutyl acrylate Polyether sulfate" 133 67 40 1. 0 05 60 Polymethyl methacrylate Polycarboxylate... 133 67 40 7 05 23 Co-polyvinylidine chloride] Polyether sulle- 133 67 40 1. 2 05 22 ethylhexyl acrylate. nate.

*At optical density=2.0.

No'rE: The dextran used in this example and in Example VII was the same as that in Example 1.

gelatin up to a concentration of 133 g. per mole of silver halide and removing a portion of the emulsion to serve as an all-gelatin control. The remainder of the emulsion was divided into a number of portions and to each portion there were added various amounts of dextran and collodially dispersed polyethyl acrylate (the 30% by weight dispersion prepared as in Procedure A) as shown in Table VI below. The emulsions were coated and evaluated as in the previous example. It can be seen that all of the emulsions having modified binders are faster and have improved density stability relative to the control. Coating No. 4 has the best over all balance of properties.

At optical density=2.0.

From the above table it is seen that all of the modified binders cause substantial improvement in wet-to-dry density stability. The best combination of properties is found in the emulsion containing polyethyl acrylate dispersed with the amphoteric dispersing agent, disodium-N- tallow-fl-iminodipropionate. By interchanging the polymers and dispersing agents still further, one can obtain various desired combinations of the properties evaluated.

Of course, various sublayers may be present to anchor the layer to the base as is common in photographic film and plate manufacture. Also, various other auxiliary layers may be employed such as antiabrasion layers and antihalation backing or undercoat layers.

The emulsions may be modified by the addition of general emulsion sensitizers, e.g., alkyl thiourea, phenyl iso-,

thiocyanate, sodium thiosulfate and alkyl isothiocyanate; metal compounds e.g., of gold, platinum palladium, iridium, rhodium, mercury, cadmium etc.; antifogging agents e.g., Z-mercaptotetrazole, benzotriazole, triazindene, tetra zindene and S-nitrobenzimidazole; sensitizing dyes; color formers, the polyoxyalkylene ethers, polyglycols, and amines disclosed in US. Patents 2,400,532, 2,423,549 and 1,925,508; hardeners, e.g., formaldehyde and other aliphatic aldehydes, dimethylol urea, trirnethylol melamine; chrome alum and other chromium compounds; coating aids, image color modifiers, brightening agents, colorants, e.g., pigments, matting agents and other emulsion adjuvants.

Photographic requirements of graphic arts emulsions are often best met by silver halides in which the predominant halide is bromide. Up to 10. mole percent iodide is added to vary the photographic behavior as well as the usual chemical sensitizers and optical sensitizing dyes. However, the unique binder advantages of this invention such as improvements in wet-to-dry density stability, impact resistance, dimensional stability, anchorage to the support, flatness and drying rate are also applicable in varying degrees to other halides over a wide range of compositions including silver chloride, chloro-bromide and iodochloro-bromide emulsions.

While these elements have their greatest usefulness in graphic art applications, many of the unique properties would be advantageous in other photographic films, e.g., cine, X-ray, portrait and color films. They could be used in monolayer or multilayer coated products. In general, these elements would be applicable to special processing variations used with conventional films, e.g. for dye inhibition films, preparing planographic printing plates, washofi relief films and stripping films such as for silk screen and gravure applications.

This invention has the advantage of providing superior photographic emulsions for the manufacture of films having improved physical properties and improved wetto-dry optical density stability of the developed image. Films made according to the present invention do not sufier the disadvantage of loss of optical density of the developed image during drying of the film. Among the improved physical properties, dimensional stability is particularly significant but improved flexibility and improved anchorage are also important. These advantages have been achieved without sacrifice in sensitometric or other physical properties of the film; in fact, photographic speed, as can be seen in various examples is significantly increased. The preferred classes of ionic dispersing agents disclosed in this invention make possible the formation of polymer particles of sufiiciently small size to provide a transparent film when mixed with gelatin, coated and dried.

The particularly preferred amphoteric dispersing agents used in the panchromatic emulsions, in contrast to the anionic and cationic surfactants used in previously disclosed products, do not interfere with dye sensitization. A further advantage is the simplicity of the process of this invention; since the additions are in the form of aqueous solutions and dispersions, the process can be carried out simply and economically on a commercial scale with no need for elaborate equipment such as solvent recovery systems.

Polymers are often incompatible and, therefore, mixtures of two or three polymers cause difiiculties where clarity is desired, as in photographic films. There are no reliable rules known in polymer science for predicting when compatibility will occur or What balance of properties the final polymer mixture will have. According to the present invention, however, applicants have provided a mixture of three different polymers and have found them to be compatible and to give photographic emulsions having excellent optical clarity as well as other useful photographic and physical properties. In the emulsions, in general the sum of the light absorbed and scat- 'tered by the combination of the three polymeric binder components in the absence of the silver and silver salts correspond to an optical density of not more than 0.1, which is advantageous.

What is claimed is:

1. A gelatino-silver halide emulsion comprising, in addition to the silver halide grains,

(1) an aqueous phase containing as a part thereof (a) 20 to parts by weight of gelatin and (b) 2.5 to 40 parts by weight of a water-soluble glycan selected from the group consisting of glycans of the empirical formulae where the monomeric units are naturally occurring units selected from the group consisting of aldose and ketose units and wherein n is 20 to 600, and

(2) 10 to 70 parts by weight of a non-aqueous phase dispersed in said aqueous phase and composed of water-dispersible colloidal particles of a substantially water-insoluble addition polymer of an ethylenically unsaturated monomer of molecular Weight less than 250.

2. An emulsion according to claim 1 wherein the particles of addition polymer have an average diameter less than 400 mg and an average molecular Weight of at least 10,000.

3. An emulsion according to claim 1 wherein said addition polymer is a polyalkyl acrylate, the alkyl group containing 1-8 carbon atoms.

4. An emulsion according to claim 1 wherein said addition polymer is a polyethyl acrylate.

5. An emulsion according to claim 1 wherein said glycan is dcxtran.

6. An emulsion according to claim 1 containing at least one amphoteric dispersing agent of the formula:

where R is an alkyl group of 12-18 carbon atoms, m is one of the numbers 0 and 1, p is 2m, and M is a cation selected from the group consisting of hydrogen, sodium, potassium and ammonium.

7. A photographic element comprising a support hearing at least One layer of a photographic emulsion as defined in claim 1.

8. An element according to claim 7 wherein the particles of addition polymer in the emulsion have an average diameter less than 400 mp. and an average molecular weight of at least 10,000.

9. An element according to claim 7 wherein the addition polymer in said emulsion is a polyalkyl acrylate, the alkyl group containing 18 carbon atoms.

10. An element according to claim 7 wherein the addition polymer in said emulsion is a polyethyl acrylate.

11. An element according to claim 7 wherein the glycan in said emulsion is dcxtran.

12. An element according to claim 7 wherein said emulsion contains at least one amphoteric dispersing agent of the formula:

where R is an alkyl group of 12-18 carbon atoms, m is one of the numbers 0 and 1, p is 2-m, and M is a cation selected from the group consisting of hydrogen, sodium, potassium and ammonium.

References Cited by the Examiner UNITED STATES PATENTS 3,000,740 9/61 De Belder et a1. 961l4 3,063,838 11/62 Jennings 9694 References Cited by the Applicant UNITED STATES PATENTS 3,069,267 12/62 Chambers. 3,085,009 4/ 63 Chambers. 3,085,010 4/63 Chambers. 3,087, 818 4/ 63 Chambers.

NORMAN G. TORCHIN, Primary Examiner. 

1. A GELATINO-SILVER HALIDE EMULSION COMPRISING, IN ADDITION TO THE SILVER HALIDE GRAINS, (1) AN AQUEOUS PHASE CONTAINING AS A PART THEREOF (A) 20 TO 85 PARTS BY WEIGHT OF GELATIN AND (B) 2.5 TO 40 PARTS BY WEIGHT OF A WATER-SOLUBLE GLYCAN SELECTED FROM THE GROUP CONSISTING OF GLYCANS OF THE EMPIRCAL FORMULAE 